Combining two smoking cessation therapies may be more effective than using just one for some smokers, according to a new study.

Researchers at Duke Medicine found that combining two smoking cessation therapies is more effective than using just one for male and highly nicotine-dependent smokers who were not initially helped by the nicotine patch.

"The findings offer a potential practical treatment approach that can identify smokers who don't respond to a single conventional treatment, but may benefit enormously from a combination of treatments," said Jed Rose, director of the Duke Center for Smoking Cessation and the study's lead author.

Rose and his colleagues have developed adaptive models for smoking cessation that tailor treatment regimens based on a person's likelihood of successfully quitting.

Smokers start using a nicotine patch prior to quitting, and based on their reduction in smoking, researchers then determine who is likely to successfully quit with or without additional treatments.

"Using a safe and inexpensive nicotine patch, we can predict a smoker's success or failure," Rose said.

"If a smoker has a low likelihood of succeeding, we can avert failure before it happens using a step-by-step algorithm to switch a smoker to a treatment that's more likely to help," Rose added.

Current smoking cessation treatments - including nicotine replacement, bupropion (sold under the brand name Zyban) and varenicline (sold as Chantix) - have modest long-term success rates.

Research has shown that less than 25 per cent of smokers remain abstinent a year after treatment.

To measure the benefit of combining treatments, the researchers enrolled 349 adults who reported smoking 10 or more cigarettes a day.

A six-item questionnaire measured the smokers' level of nicotine dependence. All participants were given nicotine patches prior to quitting.

After a week on the nicotine patch, the 222 participants who did not cut their smoking by 50 per cent while on the patch were randomly assigned to take either varenicline and a placebo or a combination of varenicline and bupropion.

The participants took the assigned treatments for 12 weeks, and were followed periodically for six months. The varenicline and bupropion were generally well tolerated, with side effects including headache, dry mouth, irritability, insomnia, vivid dreams and changes in taste.

The researchers observed an overall benefit of adding bupropion to varenicline, with 39.8 per cent of participants on the combination treatment abstaining from smoking at weeks 8-11 after the target quit date, versus 25.9 per cent taking varenicline alone.

The combined treatment had a much greater effect on male smokers and those highly dependent on nicotine, while no significant difference was seen in female smokers or those with lower levels of nicotine dependence.